1. Field of the Invention
The present invention relates to an antenna device having a balanced feed antenna and a communication device using the same.
2. Description of the Related Art
Among recent mobile communication systems, particularly among TDMA communication devices (portable telephone sets) based on the TDD (Time Division Duplex) system, communication devices each having a constitution in which an antenna is directly connected to the filter in the high-frequency circuit thereof, are increasing in number.
On the other hand, as antennae provided on the terminal equipment of mobile communication systems, for example, loop antennae or half-wave dipole antennae, which use a half-wave element, are hardly subjected to external effects. They provide characteristics more stable than quarter wave antenna.
However, the loop antenna or the half-wave dipole antenna is a balanced feed antenna, from which the output becomes balanced, and hence requires a balanced-to-unbalanced transformer (balun) for establishing the connection with the high-frequency circuit which processes unbalanced signals.
In such a structure using the balanced-to-unbalanced transformer, problems occur in that not only the number of components to be used is increased and the footprint thereof on a substrate is enlarged, but also a conversion loss is caused.
Accordingly, it is an object of the present invention to provide an antenna device and a communication device in which the problem caused by separately providing the above-described balun has been solved.
It is another object of the present invention to provide an antenna device and a communication device which allows this antenna device and communication device to be reduced in size in its entirety by reducing the space required for the above-described antenna and the filter portion directly connected thereto.
In accordance with a first aspect of the present invention, there is provided an antenna device comprising a first resonator formed by opening both ends of a xcex/2 TEM resonator; a second resonator formed by opening both ends of two xcex/4 TEM resonators which are connected together, or formed by opening both ends of a xcex/2 TEM resonator; a filter in which the first and second resonators are coupled together, in which a portion connected to the vicinity of one of the open ends of the first resonator is used as an unbalanced input-output portion, and in which a portion connected to the second resonator is used as a balanced input-output portion; and a balanced feed antenna coupled with the balanced input-output portion.
In accordance with a second aspect of the present invention, there is provided an antenna device comprising a first resonator formed by short-circuiting both ends of two xcex/4 TEM resonators which are connected together, or formed by short-circuiting both ends of a xcex/2 TEM resonator; a second resonator formed by opening both ends of two xcex/4 TEM resonators which are connected together, or formed by opening both ends of a xcex/2 TEM resonator; a filter in which the first and second resonators are coupled together, in which a portion connected to the vicinity of the equivalent open end of the first resonator is used as an unbalanced input-output portion, and in which a portion connected to the second resonator is used as a balanced input-output portion; and a balanced feed antenna coupled with the balanced input-output portion.
In accordance with a third aspect of the present invention, there is provided an antenna device comprising a first resonator formed by short-circuiting one end of xcex/4 TEM resonator; a second resonator formed by opening both ends of two xc2xc TEM resonators which are connected together, or formed by opening both ends of a xcex/2 TEM resonator; a filter in which the first and second resonators are coupled together, in which a portion connected to the vicinity of the open end of the first resonator is used as an unbalanced input-output portion, and in which a portion connected to the second resonator is used as a balanced input-output portion; and a balanced feed antenna coupled with the balanced input-output portion.
In accordance with a fourth aspect of the present invention, there is provided an antenna device comprising a first resonator formed by opening both ends of two xcex/4 TEM resonators which are connected together, or formed by opening both ends of a xcex/2 TEM resonator; a second resonator formed by opening both ends of two xcex/4 TEM resonators which are connected together, or formed by opening both ends of a xcex/2 TEM resonator; a filter in which the first and second resonators are coupled together, in which a portion connected to the vicinities of the open ends of the first resonator is used as a first balanced input-output portion, and in which a portion connected to the vicinities of the open ends of the second resonator is used as a second balanced input-output portion; and a balanced feed antenna coupled with the first or second balanced input-output portion.
By these structures, using the unbalanced input-output portion and balanced input-output portion, a balanced-to-unbalanced transformation is performed, a predetermined frequency band is passed and attenuated, and a balanced feed to the antenna is performed. Specifically, when the present antenna device is used as a reception antenna device, a balanced signal is output as an unbalanced signal from the antenna through the filter. Conversely, when the antenna device is used as a transmission antenna device, an unbalanced signal is input, fed in a balanced manner to the antenna through the filter, and an electromagnetic wave is emitted.
This eliminates the need for a balanced-to-unbalanced transformer dedicated to the present antenna device. Furthermore, since the filter and the antenna are integrated, the number of components to be used is reduced, and the footprint on the substrate in a communication device is decreased.
Preferably, each of the above-described xcex/2 TEM resonator and xcex/4 TEM resonator comprises a microstrip line and a strip line, or comprises a dielectric coaxial resonator formed by providing a conductor film on the dielectric block.
The present invention, in a fifth aspect, provides an antenna device comprising a filter having a resonator which resonates in modes other than the TEM mode and which is constructed by forming a conductor film on the outer surface of a dielectric block, and having a balanced input-output portion coupled with the resonator; and a balanced feed antenna coupled with the balanced input-output portion. These features allow this antenna device to be used even in a high-frequency band such that the filter is difficult to form in a TEM mode resonator.
Also, in the present invention, preferably an antenna device formed integrally with the dielectric duplexer is obtained by making a dielectric duplexer of the above-described dielectric filter.
Also, in the antenna device in accordance with the present invention, preferably the dielectric filter and the antenna are integrated by connecting the balanced input-output portion of the dielectric filter and the balanced feed antenna on the line of a substrate. For example, when mounting this antenna device on the circuit board of a communication device, the terminal provided on the substrate of the antenna device is made conductive to the terminal provided on the substrate of the communication device.
Furthermore, in the antenna device in accordance with present invention, preferably the balanced input-output portion of the dielectric filter and the balanced feed antenna are directly connected together by bonding the dielectric filter and the antenna. This structure allows the dielectric filter and the antenna to be separately produced, and enables the dielectric filter and the antenna to be integrated without the need for using other components such as a substrate.
Moreover, in the antenna device in accordance with present invention, preferably the balanced feed antenna is constructed on the dielectric block in which a balanced feed terminal is formed on the outer surface thereof. This facilitates mounting the antenna on the substrate, or facilitates bonding the antenna to the dielectric filter provided on the dielectric block.
Besides, in the antenna device in accordance with the present invention, preferably the balanced feed antenna and the dielectric filter are formed integrally with the dielectric block. This reduces the number of components to be used, and significantly decreases the footprint of the communication device on the substrate.
Also, in the antenna device in accordance with present invention, preferably the effective permittivity of the dielectric block is made different between the balanced feed antenna portion and the dielectric filter portion on the dielectric block, with which the balanced feed antenna and the dielectric filter are formed integrally. This allows the each of the antenna and the dielectric filter to be formed with respect to the dielectric block which has the respective optimum dielectric constants in the antenna portion and the dielectric filter portion thereof, and allows an high-efficiency antenna and a dielectric filter applied to a predetermined frequency band to be formed within a limited space.
The communication device in accordance with the present invention is constructed using the above-described antenna device. This allows a compact and lightweight communication device having a superior stability to be achieved.
The above and other objects, features, and advantages of the present invention will be clear from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings.